The proposal is aimed at understanding the neural basis of numerical processing. To accomplish this, animal subjects will be trained to categorize a visual cue on the basis of the number of times it flashes. They will report whether the number of flashes is greater or less than five by making an eye movement to one of two possible visual targets that correspond to the choices. Other stimulus dimensions of the number cue will be controlled to insure that decisions are based on number. Parietal cortex has been implicated in both numerical processing and decision-making. It is hypothesized that temporary inactivation of posterior parietal cortex (PPC) will interfere with the ability to form decisions on the basis of number, but not color, information. Neurons in PPC respond to visual stimuli in a selective region of space and before eye movements to that location, the response field (RF). The responses of neurons in PPC suggest that they integrate information in order to guide eye movements. The activity of single PPC neurons will be recorded to determine if they represent the number cue itself and decisions about number. To gain insight into how number is represented in neural structures, the number cue will be placed in the neuron's RF and the profile of activity associated with number will be quantified. In addition, the choice target will be placed in the neuron's RF to measure neural activity associated with the integration of discrete pulses of information that guide the animal's choice.